Multi-group transmissions consist of two or more transmission groups usually arranged in series, by the combination of which a large number of gears can be produced. Increasingly, they are designed as automated manual transmissions consisting, for example, of an input group, a main group and a downstream group. Such transmissions are used in particular in utility vehicles, since they provide a particularly fine gear gradation, for example with 12 or 16 gears, and their efficiency is high. For a smaller number of gears, configurations with only a main group and an input group or a main group and a downstream group are also possible. Furthermore, compared with manual-shift transmissions they are characterized by high operating comfort, and compared with automatic transmissions their production and operating costs are particularly economical.
By virtue of their structure conventional multi-group manual transmissions, in common with all manual or automated shift transmissions shifted while not under load, are characterized by an interruption of traction force during a gearshift, since the force flow from the drive motor is always interrupted by disengaging a clutch in order to disengage the currently engaged gear while free from load, synchronize the transmission and drive motor to a connection speed while in a neutral position, and then engage the target gear. Due to the coasting of the vehicle while the traction force is interrupted, undesired increases or loss of speed can occur and in addition the fuel consumption can increase. Whereas in passenger automobiles, by affecting the driving dynamics such traction force interruptions as a rule have no more than an annoying effect, for example in a sporty driving style during upshifts, in the case of heavy utility vehicles the driving speed can decrease to an extent which makes it impossible to carry out a selected gearshift and, on uphill stretches, results in undesired downshifts, crawling, or even additional starting processes.
From DE 10 2006 024 370 A1 by the present applicant an automated group-shift transmission with traction force support during gearshifts is known. The transmission comprises a splitter group as the input or upstream transmission, a main transmission as the basic transmission and a range group as the output or downstream transmission. The design of the known multi-group transmission with its input and main transmissions enables a direct gear to be engaged as an intermediate gear during a gearshift. To do this a direct connection is temporarily formed by a powershift clutch between an input shaft of the input transmission and a main shaft of the main transmission. This frees the main transmission and the splitter group from load, so that the gear engaged can be disengaged, the transmission synchronized and the target gear engaged without having to disengage the starting clutch. During this the powershift clutch transmits motor torque to the transmission output and dynamic torque that becomes free during a speed decrease between the initial and target gears is used to largely compensate for the loss of traction force. The powershift clutch, which functions as an intermediate clutch, can be positioned between the input and main transmissions or between the starting clutch provided as in a conventional transmission and the input transmission.